A brake pedal position sensor senses a position of a brake pedal and sends an electrical signal to an engine control module indicating the current position of the brake pedal. The electrical signal varies within a normal operating range with the change in position of the brake pedal. The electrical signal may be defined as operating in-range when the electrical signal is within the normal operating range.
The engine control module includes onboard diagnostics that continually monitor the electrical signal from the brake pedal position sensor. When the electrical signal from the brake pedal position sensor is out of the normal operating range, i.e., out of range, the onboard diagnostics may easily determine that the brake pedal position sensor is not functioning properly. However, the electrical signal from the brake pedal position sensor may be shorted in such a manner so as to provide a continuous and steady signal to the engine control module that is within the normal operating range, i.e., in-range. Accordingly, the onboard diagnostics are unable to detect that the brake pedal position sensor is not functioning properly because the electrical signal is in-range.
Some vehicles may employ an erratic sensor diagnostic system. The erratic sensor diagnostic system detects a fluctuating electrical signal from the brake pedal position sensor that would not be possible when actuated by an operator's foot. However, as noted above, if the electrical signal form the brake pedal position sensor is shorted in such a manner as to provide a continuous and steady electrical signal, the erratic sensor diagnostic system is unable to identify the malfunctioning brake pedal position sensor. Another method of detecting in-range brake pedal position sensor failures includes comparing the signal from the brake pedal position sensor to a signal from a second or redundant sensor that is designed to correlate with the brake pedal position sensor. However, such redundancy, i.e., a second redundant brake pedal position sensor, is not always available.